Heat up a big frying pan over medium high heat and add the meat and seasonings and cook until the meat no longer looks pink. You can break it up a bit as you are cooking it.
Add the vegetables and cook for 5-7 minutes longer.
Stir in the tomato paste and stir and cook for a few minutes more.
Add the stock, reduce the heat, and simmer uncovered for 15-20 minutes.
In another pot, cover the potatoes with water, plus 1 teaspoon salt and boil until they are tender about 20 minutes. Drain well and put them back into the pot with the butter and 2/3 cup of the cheese, and thyme.
Mash until smooth.
Add salt and pepper to your taste.
Spoon the meat mixture into a deep dish pie pan or a large baking dish. Cover with the potato mixture and sprinkle the remaining 1/3 cup of cheese over the top.
Bake for another 30 minutes.